EMV Parameters and EMV Keys Rotation

The general assumption is EMV certification process includes just two basic stages: host certification and terminal certification. Respective information can be found in our respective articles here and here. However, there is another process which is also required to ensure normal functioning of EMV processing logic.

Somehow this third process is often neglected and many developers realize its importance at late stages of EMV functionality implementation. This can lead to considerable shifts of implementation deadlines. In this article we are trying to explain the essence of the process and help those who need to implement it when the time comes. The issue is particularly relevant for those who want to support more than one acquirer.

In order for EMV kernel logic embedded in payment terminal software to function properly, it needs a set of EMV application parameters and certificate authority (CA) keys. The CA keys are involved in the interaction between the EMV kernel of the terminal and the chip.

Quite often (for example, in Verifone and Ingenico terminals) the EMV kernel is going to use XML configuration file. The file includes the information on application IDs (AID), which are going to be supported by the terminal, respective parameters and keys for these AIDs.

EMV parameters are not changed very often (if changed at all). Most processors provide these parameters in pdf format. Usually, a pdf file is a contextual document, where they can be found. On their basis an XML file can be assembled.

Importance of EMV keys rotation: EMV certification perspective

In contrast to parameters, CA keys have to be changed (rotated) regularly. Most processors usually provide some sort of API (as a rule, it is a part of the main processing specification), including a subset of functions, dedicated to loading of the CA keys. Some processors will provide the initial set of keys through a document and require you to load updated keys using the API. Some processors will tell you initially to get all the keys by making a respective API call. Therefore, it is important to allocate time and resources for the implementation of this logic from the very beginning of your project planning, because there is no equivalent for this in card-not-present integrations or swipe integrations.

As we can see, in addition to host integration and terminal integration (with subsequent certifications), you also have to implement the rotation procedure for CA keys. Some of the processors will leave it up to you to implement this and will not require you to formally certify the process. Some of the processors (such as Chase Paymentech) will actually require you to demonstrate (during the certification process) that you can dynamically change the keys as transactions are getting processed.

Generally, the functionality around key rotations is appropriate for payment terminal management systems (TMS), and the function will be available in the TMS that you use. However, if you are not using any TMS, or TMS is unavailable for you, you can implement the respective logic as part of payment gateway functionality. The implementation process will depend on the number of different processors that you support and on the differences between application parameters (such as floor limit) across payment terminals. Implementation can be as simple as a file download from a server over FTP, where the file gets re-generated every time you get a different set of keys from the processor. It can be as complex as an API call where terminal identifies itself and then terminal-specific configuration file is assembled based on the most up-to-date information available from the processor that this terminal uses.

Conclusion

It is extremely important to allocate the time and resources for implementation of EMV keys rotation logic even for the most basic EMV certification. Even if you are not required to present the logic at certification stage, you are definitely going to confront the issue during production. While expiration period for a some of the keys can be up to 24 months, you will not necessarily have all that time before the initial key rotation has to be done.